1. Field of the Invention
The invention concerns particles of luminescent carbon, which can notably be used in the field of counterfeiting prevention.
2. Description of Related Art
Luminescence is the emission of light in a rapid manner (fluorescence) or slower manner (phosphorescence) subsequent to the absorption of photons by a molecule previously having been excited.
The luminescent particles can be incorporated within an ink, thus allowing objects to be marked. They can thus provide a means of identification that is generally invisible to the naked eye, with detection possibly requiring a specific wavelength of excitation.
Such is notably the case with fluorescent particles.
The fluorescent properties of particles of homogeneous composition in accordance with past art are generally conferred during their synthesis. However, this solution is not suitable for the preparation of black inks, which absorb all wavelengths of excitation. The fluorescence of particles according to prior art is therefore annihilated when they are used for preparing a black ink, because the excitation energy is absorbed by the black color.
To overcome this, metallic particles having a structure of core/shell type have been developed. Notably, cobalt/carbon particles are employed, of which the carbon shell has been functionalized at the surface by means of hybrid groupings such as the association of pyrene and BODIPY.
The BODIPY groupings responsible for the fluorescence are thus distanced from the core of the particle, so as to prevent the phenomena of “quenching” (deactivation) of the fluorescence.
However, these particles require a process of synthesis that is painstaking as regards the steps of preparation of metallic particles, of the coating of the metallic particles, and of the functionalization of the coating by means of a hybrid mixture of compounds. The synthesis involves multiple stages and is difficult.
The Applicant has developed luminescent particles of carbon that allow the preparation of a black ink with luminescent properties.
Furthermore, the process of preparation of these particles allows one to adapt the nature of the surface of these particles for their usage, without requiring a complex functionalization stage.